error[E0502]: cannot borrow `slice_1` as immutable because it is also borrowed as mutable
 --> compile_fail_tests/mut_lock_6.rs
  |
  |     let mut a = slice_1.iter_mut();
  |                 ------------------ mutable borrow occurs here
  |
  |     let _ = slice_1.get(1).unwrap().borrow();
  |             ^^^^^^^^^^^^^^ immutable borrow occurs here
  |
  |     a.next().unwrap().borrow();
  |     -------- mutable borrow later used here